For a central air conditioning system, a chiller is typically used as a cooling apparatus. Cold water is produced by the chiller and conveyed through pipes to decrease room temperature by heat exchange. The chiller has become widely used in recent years, and a compressor is a core operating component of the chiller. For example of a centrifugal compressor, surge usually occurs in the centrifugal compressor during operation, which not only generates noise but also aggravates the stress exerted on the driving motor and the vane bearing of the centrifugal compressor, thereby leading to damage to the centrifugal compressor. The longer the surge lasts, the more damage is dealt to the centrifugal compressor.
A surge detection method is employed currently to eliminate surge in the centrifugal compressor, which involves measurement of a single variable (such as current, temperature, or pressure) and signal processing of the measured variable to determine the occurrence of surge. U.S. Pat. No. 5,746,062 discloses such method, which analyzes a single variable and uses a threshold value as a basis of determination. As shown in FIGS. 4(a) and 4(b) of this patent, to acquire accurate and stable values for determination, after the difference in pressure is obtained by a sensor followed by a series of complicated logical determination processes are performed in order to avoid false judgment. Whether surge occurs or not can be confirmed in the centrifugal compressor by the result. The above surge detection method, however, is very complex and is time and cost-ineffective. Furthermore, the above method detect surging when it has occurred in the centrifugal compressor, and such time delay of surge determination could be accompanied with damage to the centrifugal compressor.
Therefore, the problem to be solved here is to develop a method for predicting surge in a compressor, which can overcome the aforesaid drawbacks of the prior art.